Modern research has suggested that cranberry may prevent urinary tract infections.^13,14 In a double-blind trial, elderly women who drank 10 ounces (300 ml) of cranberry juice per day had a decrease in the amount of bacteria in their urine.¹⁵ In another study, elderly residents of a nursing home consumed either four ounces (120 ml) of cranberry juice or six capsules containing concentrated cranberry daily for 13 months. During that time, the number of UTIs decreased by 25%.¹⁶ A small preliminary trial found that supplementation with encapsulated cranberry concentrate (400 mg twice per day for three months) significantly reduced the recurrence of UTIs in women (aged 18 to 45) with a history of recurrent infections.¹⁷

Cranberry juice has also been found to be as effective as the antibiotic cefaclor for preventing UTIs in children who had recurrent UTIs because of a condition that causes urine to flow backwards from the bladder into the ureters (vesicoureteral reflux). In that study, the children received a cranberry juice concentrate that was equivalent to 200 ml of cranberry juice per day.¹⁸

Research has suggested cranberry may be effective against UTIs because it prevents E. coli, the bacteria that causes most urinary tract infections, from attaching to the walls of the bladder.¹⁹ Cranberry is not, however, a substitute for antibiotics in the treatment of acute UTIs. Moreover, in children whose UTIs are due to “neurogenic bladder” (a condition caused by spinal cord injury or myelomeningocele), cranberry juice supplementation did not reduce the rate of infection.²⁰ Drinking 10–16 ounces (300–500 ml) of unsweetened or lightly sweetened cranberry juice is recommended by many doctors for prevention, and as part of the treatment of UTIs. Alternatively, 400 mg of concentrated cranberry extracts twice per day can be used.